Navigation-protractor.



v F. W. STERLING & R. A. KOCH.

NAVIGATION PROTRACTDH.

APPLICATION FILED AUG-I6. 1913.

tfllqil Patented May15,1917.

/ WWW 22f for" UNITED STATES" PATENT OFFICE.

mum: w. s'rnnnme AND RALPH A. noon, on THE UNITED sm'rns saw.

NAVIGATION-PROTRACTOR.

Specification of Letters Patent.

Application filed August 16, 1913. Serial No. vsamoi.

To all whom it may concern:

'Be it, known that we, FRANK W. STER- LING and RALPH A. Koori, both citizens of and consists of improved means for use in solving on a chart the problems of navigation. The invention herein-described, illustrated and claimed may be made or used by the Government of the United States or any of its ofiicers, employees, or contractors, in the prosecution of work for the United States Government, without the payment of across its face, and an index mark 9 at the middle of one side, and the tabs 10 for convenience in turning. The cards may be pivotally and centrally mounted in any suit I able manner such as around a hollow centrally apertured boss 3 where they are held between a flange 5 at the lower end and a nut 13 screwing'on the shank 6 of the boss.

7 If desired the compass card may be attached set position.

in any suitable manner to the flange.

While any desired number of pointer arms may be pivoted to the boss, in the drawing illustrating our invention three arms 4, are shown separated by washers 14 and held pivotally mounted between the nut 13 and a nut 15 screwing on the upper end of the shank; It will be seen that the frictional contact between the two cards may be adjusted by the lower nut 13, which has radial holes 18 for a key. tween the arms is independently adjustable by the upper nut 15 until any arm can be set without interfering with the other arms, or the'arms may be simultaneously locked in One or more arms may be taken off the boss. The pointer arms extend ing beyond the cards have-one edge 16 in 1 line with the center straight and another Our invention relates to navigation plots The friction beedge 17 out of such alinement mutilated or indented to avoid all danger of using. Other means such as a dark strip along that edge could be employed.

The construction of the protractor is such as facilitates the setting of the arms and cards, the adjustment of the frictional contact, and the simultaneous locking of the arms. The straight sides of the rectangular card cooperate with the parallel lines on its face, which show through the transparent protractor on to the chart, in enabling the protractor to be easily oriented without the necessity; of using the chart compass rose on whatever part of the chart the protractor may beplaced.

In determining the ships position from two bearings the third arm is useless and may be removed the index mark on the rectangular card is set the given amount to correct for compass error, and two pointer arms set to the bearings, accurately shifting the protractor about the chart until the straight edges of the pointer arms out through the landmarks observed, and the sides and lines of the rectangular card parallel the meridians and parallels of the chart after which the ships position is easily and quickly plotted through the central aperture of the boss. To reverse the problem and determine the compass error on any course from three bearings, the pointer arms are set and the protractor shiftedabo'ut on the chart until all the pointer arms out in. Then by holding the compass card down on the chart the upper rectangular card may be turned until its sides and lines parallel those on the chart when the reading of its index gives the desired compass error. The use of the protractor in determining courses, and in solving other problems in'navigation will be apparent.

Having thus described our invention what we claim and desire to secure by Letters Patent is 1. In a navigation protractor, a boss, two

- cards pivotally mounted on said boss, means for simultaneously adjusting the frictional Patented May 15, 1917.

mounted on said boss, means for adjusting the frictional resistance to rotation of said cards and independent means for adjusting the frictional resistance to rotation of said pointer arms. 0

3. In a navlgatlon protract'or an outwardly threaded apertured boss flanged at its lower end and a transparent circular cornpass card, a transparent rectangular card superposed thereon, both pivotally and cen-v trally mounted on said boss, a nutscrewed on to the boss for adjusting the frictional contact between the two cards, three trans parent pointer arms revolubly mounted on said boss above said nut, a plurality of washers separating the pointer-arms, and a nut screwed on the upper end of the boss for locking and adjusting the frictional resistance to rotation of said pointer arms.

4. In a navigational protractor acentral boss having an outwardly threaded portion;

tw'o cards, both pivotally and centrally mounted on said boss, a plurality of radialarms similarly monnted on. said boss, and two nuts screwlng on said boss, one for adustmg the resistance to rotation of the cards, and the other for similarlyadjusting the resistance to rotation of the arms. p In testlmony whereof we aifix our signatures 1n presence of two witnesses.

FRANK w. STERLING. rRALPH A. KOCH.

{ for FrankW. Sterling 

